This proposal will examine changes in astrocytes during aging. The primary aim is to test the hypothesis that some age-related changes in neurochemical markers are secondary to an increase in the fractional volume of brain occupied by astrocytes. Four specific studies are proposed: Study I: The age-related increase in GFAP mRNA will be quantified precisely using solution hybridization. GFAP protein levels will be measured by immunoassay to determine if the increases in RNA translate into increased protein content. Immunohistochemical and in situ hybridization techniques will estimate the fractional area of sections staining positively for GFAP and the staining intensity of astrocytes. Regional variations in enhanced GFAP expression with age will be explored. Study II: A specific astrocyte lesion preparation will be characterized. This preparation will be contrasted with selective neuronal lesions (ibotenic acid) in various brain regions during aging. Neurochemical markers will be examined to determine their astrocytic vs. neuronal localization in young and old rats. Study III: A mouse model of the human premorbid agonal condition will be studied for regulation of GFAP RNA expression and protein levels using the same techniques in study 1. The proximate cause of the increase in GFAP-RNA in these wasting mice will be sought by examining select aspects of the model; food deprivation, tumor transplantation, immune system reactivity and other conditions will be tested. Study IV: Intrinsic vs. extrinsic regulation of astrocyte phenotype with age will be studied by a) culturing astrocytes from young and old donors and comparing GFAP expression and cell size (also growth rate), b) grafting cultured neonatal astrocytes labeled with fluorescent microspheres into young and old hosts, and c) grafting astrocytes from young and old donors into both young and old hosts.